Fuel cells are advantageous in that they require substantially no fossil fuel (whose depletion in the near future is feared) and, when used for power generation, generate substantially no noise and are high in energy recovery as compared with other methods for power generation. Therefore, fuel cells are being developed as a power generation plant of relatively small size for buildings and factories.
Among fuel cells, a solid polymer type fuel cell operates at lower temperatures than other type fuel cells do; therefore, it has such characteristics that not only the parts constituting the cell are little corroded, but also the cell can discharge a relatively large electric current for the low temperature operation. Therefore, the solid polymer type fuel cell is drawing attention as a substitute electric source for internal combustion engine of vehicle.
Among the parts constituting the above solid polymer type fuel cell, the separator has a role of transferring the electricity generated at the gas diffusion electrode of fuel cell to the exterior and also a role of discharging the water formed in the course of electricity generation to secure a flow path for a reactant gas which is allowed to flow into the fuel cell. Accordingly, the separator for solid polymer type fuel cell is desired to have high drainability.
Therefore, as the fuel cell separator, there have heretofore been used those subjected to a hydrophilization treatment owing to this hydrophilization treatment, the water formed does not remain as droplets and is moved to a given position of the flow path, whereby the diffusion of reactant gas is not hindered by the formed water.
In order to specifically make the fuel cell separator hydrophilic, there were proposed, for example, a method in which a material for fuel cell separator is molded into a predetermined shape and thereafter the molded material is coated with a hydrophilic material (e.g. a polyacrylonitrile) and a method in which a hydrophilic material is incorporated into a material for fuel cell separator and the resulting material is molded into a predetermined shape.
However, it is pointed out that the conventional methods mentioned above have the following problems.
As to the method in which a material for fuel cell separator is molded into a predetermined shape and thereafter the molded material is coated with a hydrophilic material (e.g. a polyacrylonitrile), it is pointed out that the coating with the hydrophilic material gives a separator having an insulating film made of the hydrophilic material, on the whole surface and this insulating film must be removed at the portions of separator contacting with the gas-diffusion electrode of fuel cell, resulting in an increase of cost.
Moreover, as to the method in which a hydrophilic material is incorporated into a material for fuel cell separator and then the resulting material is molded into a predetermined shape, it is pointed out that although cost reduction can be expected, the resistivity of the whole separator is increased because ordinary hydrophilic materials have no electrical conductivity, and the performance of the fuel cell is deteriorated.
Therefore, the solution of the above problems has been desired.
The present invention aims at alleviating the above-mentioned problems of the prior art and providing a fuel cell separator which is low in cost and high in hydrophilicity and electrical conductivity and a process for production of such a fuel cell separator.